The present invention relates to a method for cutting freeform surfaces by milling. In addition, this invention relates to a device for cutting freeform surfaces by milling.
The present invention relates to the field of cutting technology, in particular by HSC (high-speed cutting), also known as HPC (high-performance cutting).
In cutting freeform surfaces by milling, a tool called a milling cutter is moved in relation to the workpiece. Cutting causes wear on the tool, namely the milling cutter, so the milling cutter must be replaced at certain intervals or must be reground. This may result in changes in dimension of the tool, i.e., the milling cutter. Taking into account, i.e., compensating for deviations in dimensions, changes in dimensions of the milling cutter during cutting is known as radius correction, i.e., cutter radius correction.
Cutting machines and/or NC controls for cutting machines that allow such a cutting radius correction in 3-axis cutting are known in the state of the art. In 3-axis cutting, the milling cutter is moved in three translational axes in relation to the workpiece to be machined. If such a milling cutter radius correction is performed in 3-axis cutting, it is a 2D-radius correction.
Complex freeform surfaces such as those encountered in the manufacture of rotors having integral blades, for example, must be performed with the help of so-called 5-axis cutting, i.e., in addition to the movement of the milling cutter along the three translational axes, movement thereof along two rotational axes is also required. According to the state of the art, it has not so far been possible to utilize a radius correction function in 5-axis cutting. A correction in 5-axis cutting would be a 3D-radius correction.
Against this background, the object of the present invention is to provide a novel method for cutting freeform surfaces and a corresponding device.
According to this invention, a tool vector in the form of leading angles and setting angles is defined for each interpolation point on the tool path. In addition, a normal vector is determined for each interpolation point from the leading angles and the setting angles as well as from a drive vector determined for each interpolation point. The normal vector at each interpolation point of the tool path is used for a 3D-radius correction for equalizing deviations in dimensions of the milling cutter. With the help of the invention as proposed here, it is possible for the first time to perform a radius correction, namely a 3D-radius correction, in 5-axis cutting.
According to an advantageous refinement of the present invention, to determine the normal vector for each interpolation point, in a first step the tool vector of the particular interpolation point is rotated back about the corresponding drive vector by the amount of the particular setting angle, thus yielding a first intermediate vector for the particular interpolation point. Then, in a second step, the cross product of the first intermediate vector of the particular interpolation point and the drive vector of the particular interpolation point is formed, this cross product yielding a second intermediate vector for the interpolation point. Then, in a third step, the first intermediate vector of the particular interpolation point is rotated back about the second intermediate vector of the particular interpolation point by the amount of the particular leading angle, thus yielding the normal vector for the interpolation point.
Preferred embodiments of this invention are derived from the following description.